unable to add any repository via add-apt

I have same computer, installed from same image as my college, but yet I'm not able to add new repositories to ubuntu. I'm not aware of any relevatn modifications made to the system, and I'd really like to avoid reinstall. Is there any way how to add new apt repositories to 18.04

sudo add-apt-repository ppa:freecad-maintainers/freecad-daily
LSB codename: 'bionic'.
This codename isn't currently supported.
Please check your LSB information with "lsb_release -a".

mmucha@utu:/etc/apt/sources.list.d$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.1 LTS
Release:    18.04
Codename:   bionic

if I add that repository manually, there is missing GPGkey or invalid, but I have no idea how to download GPG for ppa... Details of failing GPG here: fingerprint-gui in 18.04

maybe related question: Software & Updates missing from Applications dashboard

Try adding the PPA manually. Create a file in the /etc/apt/sources.list.d directory called freecad.list.

Note you can really name the file whatever you like but it needs to be in that directory and it needs to have a .list extension. Put this in the file:

deb http://ppa.launchpad.net/freecad-maintainers/freecad-daily/ubuntu bionic main 
deb-src http://ppa.launchpad.net/freecad-maintainers/freecad-daily/ubuntu bionic main